Augers are well recognized drilling tools capable of simultaneously drilling and casting a hole in various types of earth constituents. The hollow stem auger is used primarily in the environmental and construction industry and employs a large tubular shaped drilling device that allows for the insertion of core items therein. To allow for ease of a core item insertion, an end cap is provided at the end of a cutting head that is removed after the drilling operation.
The cutter head is critical to the drilling operation employing a variety of cutting bits capable of penetrating the soil when coupled to a conventional drill rig. The cutter head is rotated by the drill rig wherein the cutting bits cooperate to break up the soil during insertion. An auger provides movement of material around the diameter of the drilling rig during insertion and commonly include a flighting section for transferring material upwardly so as to avoid impacting.
A drilling machine is used to force the cutter head into the ground which causes the cutting bits to loosen ground materials such as clay, granite, and the like encountered during the drilling process. Once the cutter head has reached a desired depth, the hollow stem may be used as a central passageway for insertion of a separating screen. The screen is inserted through the hollow stem of the auger and used to knock out the end cap centrally located on the end of the cutter head. The end cap remains at the bottom of the drilled hole while the auger device is removed. Back filling of the hole around the screen is possible while the end cap remains at the bottom of the hole, the screening separating the surrounding soil thereby maintaining a hole for insertion of sampling instruments.
A problem with the hollow stem auger, to which this invention is directed, relates to the end cap which operates a drilling impediment and once the drilling is complete remains at the bottom of the formed hole. If constructed of wood, the end cap may interfere with sampling as wood can concentrate and retain various fluids. If constructed of plastic, the end cap does not disintegrate and operates as a form of pollution.
The use of the centrally disposed end cap places a great strain on the drilling equipment as the cutting bits located around the circumference of the cutting head are required to break up the ground during the drilling process. The end cap, having no drilling surface, operates as an outright impediment during the drilling operation as forward progress must rely upon the bits located along the circumference to loosen any materials directly in the path of the tip.
A cutter head has a flighting section and bit blocks that form the outer most section of the cutter head and are used for reaming of the hole to be drilled. This section takes a tremendous amount of wear as a result of being placed against hard formations during the rotation and advancing of the cutter head. In this manner, the conventional cutter head components tend to wear out quickly if the cutter head is used to drill in hard ground, the chisel bits may wear unevenly and have a tendency to wear on one side.
During insertion of the cutting head the end cap may impact a rock wherein forward motion can not proceed without either moving the cutter head to a new position or allowing the cutter head to "walk" wherein the chipping bits can engage the rock. In either instance, the cutter head is placed in an awkward position placing a strain on the drilling equipment. If the impact against the end cap is severe, the end cap can be dislodged resulting in leakage which may lead to failure of the drilling operation.
U.S. Pat. No. 5,158,147 attempts to address these problems by use of a cutter head having a cutting bit located on the end. The cutting head includes a flighting section mounted on the cutter body having a bit block fixed to the flighting section. The bit block works in conjunction with a first outside chisel bit for rotation about its own axis. While this invention discusses the need for placing of cutting bit along the end, it fails to address the end cap and by design eliminates its usage. The invention does not address the need for drilling operations wherein the end cap is necessary. The result limits the drilling tools effectiveness to ground formations that will not collapse during removal of the auger.
U.S. Pat. No. 5,427,191 sets forth an auger assembly capable of boring hard surfaces, namely rock. As disclosed by the invention, when hard rock formations are encountered conventional drilling rates are severely limited. The problem with the cutter head of the disclosed invention is it prohibits the use of the hollow stem auger. While the device is most beneficial for rock formations, it is unlikely that a rock formation will be found individually without some combination of loose soil. In this manner, while the instant invention may drill through rock, the associated substrate will collapse on the auger hole requiring multiple drilling if not subsequent use of hollow stem auger so as to allow the placement of sampling or testing components as typically used in a hollow stem auger application.
Thus, what is needed in the art is a hollow stem auger cutter head that maintains the use of a knock-out end cap, yet provides provisions for salvaging of the cap after use. In addition, an end cap is needed that remains an integral part of the drilling operation so as to lessen wear and increase drilling operation efficiency.